Package substrate dynamic pressure structure

ABSTRACT

Devices and methods for their formation, including electronic assemblies having a shape memory material structure, are described. In one embodiment, a device includes a package substrate and an electronic component coupled to the package substrate. The device also includes a shape memory material structure coupled to the package substrate. In one aspect of certain embodiments, the shape memory material structure is formed from a material selected to have a martensite to austenite transition temperature in the range of 50-300 degrees Celsius. In another aspect of certain embodiments, the shape memory material structure is positioned to extend around a periphery of the electronic component. Other embodiments are described and claimed.

RELATED ART

Integrated circuits may be formed on semiconductor wafers made frommaterials such as silicon. The semiconductor wafers are processed toform various electronic devices. The wafers are diced into semiconductorchips (a chip is also known as a die), which may then be attached to apackage substrate using a variety of known methods. In one known methodfor attaching a chip or die to a package substrate, the die may havesolder bump contacts which are electrically coupled to the integratedcircuit. The solder bump contacts extend onto the contact pads of apackage substrate, and are typically attached in a thermal reflowprocess. Electronic signals may be provided through the solder bumpcontacts to and from the integrated circuit on the die.

The material of package substrate typically does not provide an exactmatch with the material of the die with respect to the coefficient ofthermal expansion. Thermal expansion mismatch can lead to stressesdeveloping in the electronic assembly during processing procedures, inparticular, during heating and cooling operations such as solder reflow.Such stresses may cause warpage in the package substrate. As electronicdevices and package substrates become more thin, warpage will continueto be a problem.

Package substrate warpage problems may be addressed using a number ofapproaches. For example, a thicker substrate may be used. The thickersubstrate is more rigid due to its thickness and thus less likely toundergo substantial warpage. Another approach is to use a heat spreadercoupled to the die and the substrate. The heat spreader also makes theassembly more rigid and less prone to warpage. Still another approach isto use a stiffener coupled to the package substrate. The stiffener maytake the form of a metal ring coupled to the package substrate. Themetal ring adds mass to the assembly and makes it more rigid and lessprone to warpage. All of these methods add substantial mass andthickness to the package substrate assembly.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments are described by way of example, with reference to theaccompanying drawings, which are not drawn to scale, wherein:

FIG. 1 illustrates a shape memory material structure on a packagesubstrate, in accordance with certain embodiments;

FIGS. 2(A)-2(C) illustrate processing operations for coupling a shapememory material structure to a package substrate, in accordance withcertain embodiments;

FIG. 3 illustrates a top view of a shape memory material structure on apackage substrate, in accordance with certain embodiments;

FIG. 4 illustrates a top view of a shape memory material structure on apackage substrate, in accordance with certain embodiments;

FIGS. 5(A)-5(C) illustrate processing operations for coupling a shapememory material structure to a substrate and the resultant assemblyafter heating, in accordance with certain embodiments;

FIG. 6 illustrates a flow chart of certain operations for forming anassembly, in accordance with certain embodiments; and

FIG. 7 illustrates an electronic system arrangement in which certainembodiments may find application.

DETAILED DESCRIPTION

Certain embodiments relate to electronic assemblies. Embodiments includeboth devices and methods for forming electronic assemblies.

FIG. 1 illustrates an electronic assembly in accordance with certainembodiments. The electronic assembly includes a package substrate 10having a shape memory material structure 12 and an electronic componentsuch as a die 14 positioned thereon. The package substrate may be asingle layer or multilayer, and may be formed from any suitablematerial, including, but not limited to, ceramics, polymers, andcomposite structures. One example of a suitable package substratematerial is an epoxy resin. As illustrated in the embodiment of FIG. 1,the die 14 may be positioned on a central region of the packagesubstrate 10. The shape memory material structure 12 may encircle thedie 14 and be positioned on an outer portion of the package substrate10.

One example of a shape memory material composition includes an alloyincluding nickel-titanium and is sold under the trade name NITINOL.Shape memory materials, such as certain alloys, have the unique propertyof regaining their original shape through a phase transformation belowthe melting point. In the case of most alloys, the original shape is setat a high temperature while in the austenite crystal phase. Uponcooling, the crystal phase changes to martensite. Any changes to theshape of the material will be reset to the original shape during thecrystal structure transformation from martensite to austenite. Thistransformation imparts a force on the material. For example, a shapememory material that has experienced a strain in the martensitic phase,upon heating, may undergo a phase change to a more ordered austeniticcrystal phase. This phase change causes the material to recover itsstrain and is capable of imparting large forces. One specific example,NITINOL H (a high temperature range NITINOL) has an austenite transitiontemperature of 100 degrees Celsius, and may be used in certainembodiments. Certain embodiments utilize a shape memory materialstructure formed from a material having a martensite to austenitetransformation temperature in the range of about 50 to about 300 degreesCelsius. Shape memory materials may include, but are not necessarilylimited to, metal alloys having suitable phase transformationproperties.

The use of a shape memory material structure enables an active force tobe applied to counteract the package warpage forces during reflowtemperatures so that the package substrate assembly can remainsubstantially flat. Conventional approaches provide a passive control toinhibit warpage, whereas the use of a shape memory material structureprovides an active control, during the processing operations thatgenerate warpage forces, to inhibit warpage. The use of the active forceapplied by the shape memory material enables certain embodiments to beformed thinner than conventional stiffeners, while providing the same ora greater level or force to resist warpage (the conventional stiffenerapplies a passive force after the package substrate begins to warp). Asa result, certain embodiments are well suited to being used inapplications where limiting thickness is essential, for example, inpackage assemblies for mobile applications.

In certain embodiments, the shape memory material structure 12 may beformed and the original shape may be set at around 500 degrees Celsius,in the austenite crystalline phase. The shape memory material structure12 may in certain embodiments be formed to have a zero or near zerowarpage. The structure 12 may then be coupled to the package substrateas will be described below in connection with FIG. 2. When the packagesubstrate is exposed to elevated temperatures and starts to warp (forexample, during a reflow process), the shape memory material structure12 produces a counter force to the warpage because the elevatedtemperature is changing the crystal structure from a martensitic crystalstructure to an austenitic crystal structure. This change in crystalstructure applies an active force that suppresses the packagesubstrate's tendency to warp during elevated temperature processes.

FIGS. 2(A)-2(C) illustrate coupling the shape memory material structure12 to the package substrate 10, in accordance with certain embodiments.The shape memory material structure 12 may be coupled to the packagesubstrate using any suitable approach. As seen in FIG. 2(A), forexample, an adhesive 16 is applied to the package substrate 10 throughan applicator 15. A variety of adhesives may be used, including, but notlimited to, an epoxy adhesive. The adhesive 16 is positioned on thesurface of the package substrate 10, and then the shape memory materialstructure 12 is positioned thereon, as illustrated in FIG. 2(B).

Depending on the adhesive used, a heating operation may be carried out,as indicated in FIG. 2(C), to cure the adhesive 16 to form a suitablebond between the shape memory material structure 12 and the packagesubstrate 10. While FIG. 2(A) illustrates the use of a liquid adhesivethat is applied to the package substrate, other approaches, for example,a solid, preformed adhesive that is heated after the shape memorymaterial structure is positioned on the substrate, may also be used incertain embodiments. In an alternative embodiment, the shape memorymaterial structure 12 maybe deposited directly onto the packagesubstrate 10, with no separate adhesive layer formed therebetween.

In certain embodiments, after the shape memory material structure 12 hasbeen coupled to the package substrate 10, an electronic device such asthe semiconductor die 14 is coupled to the package substrate 10 using asuitable method, for example, a solder bump method.

The shape memory material structure may in certain embodiments have aring-like structure. By ring-like, it is meant that the structure isformed to extend around (or define) a hole or open region. In FIG. 1,the shape memory material structure 12 defines a hole bounded by thefour sides (and curved corner regions) of the shape memory materialstructure 12. The die 14 is positioned within a portion of the holebounded by the sides of the shape memory material structure 12. Theembodiments illustrated in FIGS. 1, 3, and 4 are all examples ofring-like structures.

FIGS. 3, 4, and 5(A)-5(C) illustrate additional examples of shapes andpositions of shape memory material structures on package substrates. InFIG. 3, the shape memory material structure 32 positioned on the packagesubstrate 30 has a structure that is substantially circular when viewedfrom above. In FIG. 4, the shape memory material structure 42 on thepackage substrate 40 has a structure that is substantially rectangularin structure, with rounded interior corners. The shape memory materialstructures 32, 42 of FIGS. 3 and 4 are positioned a distance away fromthe side edges of the package substrates 30, 40, unlike the shape memorymaterial structure 12 of FIG. 1, which is aligned with the side edges ofthe package substrate 10.

FIGS. 5(A)-5(C) illustrate the application of a shape memory materialstructure 52 to a substrate 50 and the resultant assembly after heating,in accordance with another embodiment. In this embodiment, the shapememory structure 52 is formed to have a curvature that opposes that ofthe substrate 50 to which it is attached. As illustrated in FIG. 5(A),the shape memory structure 52 has a curvature that is opposite thecurvature of the substrate 50. FIG. 5(B), the shape memory materialstructure 52 is coupled to the package substrate 50 and has a concaveshape due to the forces applied by the substrate 50. FIG. 5(C)illustrates the shape memory material structure 52 and substrate 50after heating, where the heating has caused a phase change in the shapememory material structure 52, which applied a force to counteract theforce in the substrate 50 and caused the assembly to flatten. Thus, theuse of a concave or otherwise bowed shape material structure may also beused in certain embodiments to provide additional force to counteractwarpage forces developed during processing operations.

FIG. 6 illustrates a flow chart of certain operations for forming anassembly in accordance with certain embodiments. Box 60 is providing apackage substrate to which a shape memory material structure and anelectronic device will be coupled. Box 62 is coupling the shape memorymaterial structure to the substrate, using a technique such as describedabove. Box 64 is coupling an electronic device such as a semiconductordie to the substrate, to form an assembly.

Assemblies as described in embodiments above may find application in avariety of electronic components. In certain embodiments, a device ordevices in accordance with the present description may be embodied in acomputer system including a video controller to render information todisplay on a monitor coupled to the computer. The computer system maycomprise one or more of a desktop, workstation, server, mainframe,laptop, handheld computer, handheld gaming device, handheldentertainment device (for example, a video player), PDA (personaldigital assistant), telephony device (wireless or wired), etc.Alternatively, a device or devices in accordance with the presentdescription may be embodied in a computing device that does not includea video controller, such as a switch, router, etc.

FIG. 7 schematically illustrates one example of an electronic systemenvironment in which aspects of described embodiments may be embodied.Other embodiments need not include all of the features specified in FIG.7, and may include alternative features not specified in FIG. 7. FIG. 7illustrates an embodiment of a device including a computer architecture100 which may utilize integrated circuit devices having a structureincluding capacitors formed in accordance with embodiments as describedabove. The architecture 100 may include a CPU 102, memory 104(including, for example, a volatile memory device), and storage 106(including, for example, a non-volatile storage device, such as magneticdisk drives, optical disk drives, etc.). The CPU 102 may be coupled to aprinted circuit board 107, which in this embodiment, may be amotherboard. The CPU 102 is an example of a package substrate assemblyformed in accordance with the embodiments described above andillustrated, for example, in FIG. 1. A variety of other systemcomponents, including, but not limited to input/output devices,controllers, memory and other components, may also include structuresformed in accordance with the embodiments described above. The systemcomponents may be formed on the motherboard, or may be disposed on othercards such as daughter cards or expansion cards.

The storage 106 may comprise an internal storage device or an attachedor network accessible storage. Programs in the storage 106 may be loadedinto the memory 104 and executed by the CPU 102 in a manner known in theart. The architecture may further include a network controller 108 toenable communication with a network, such as an Ethernet, a FibreChannel Arbitrated Loop, etc. Further, the architecture may, in certainembodiments, also include a video controller 109, to render informationon a display monitor, where the video controller may be embodied on avideo card or integrated on integrated circuit components mounted on themotherboard, for example. Other controllers may also be present tocontrol other devices.

An input device 110 may be used to provide input to the CPU 102, and mayinclude, for example, a keyboard, mouse, pen-stylus, microphone, touchsensitive display screen, or any other suitable activation or inputmechanism. An output device 112 including, for example, a monitor,printer, speaker, etc., capable of rendering information transmittedfrom the CPU 102 or other component, may also be present.

While certain exemplary embodiments have been described above and shownin the accompanying drawings, it is to be understood that suchembodiments are merely illustrative and not restrictive, and thatembodiments are not restricted to the specific constructions andarrangements shown and described since modifications may occur to thosehaving ordinary skill in the art.

1-9. (canceled)
 10. A method comprising: providing a package substrate;coupling a shape memory material structure to the package substrate; andcoupling an electronic component to the package substrate;
 11. Themethod of claim 10, wherein the electrical component and the shapememory material structure are positioned so that the shape memorymaterial structure extends around a periphery of the electroniccomponent.
 12. The method of claim 10, wherein the shape memory materialcomprises nickel and titanium.
 13. The method of claim 10, wherein theshape memory material has a martensite to austenite transitiontemperature in the range of 50-300 degrees Celsius.
 14. The method ofclaim 10, wherein the coupling a shape memory material structure iscarried out prior to the coupling an electronic component to the packagesubstrate.
 15. The method of claim 10, wherein the coupling a shapememory material structure comprises a method selected from the groupconsisting of depositing the shape memory material structure directlyonto the package substrate using a vapor deposition method, and adheringthe shape memory material structure to the package substrate using anadhesive positioned between the shape memory material structure and thepackage substrate.